Front light positition

General cycling advice ( NOT technical ! )
Oldjohnw
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Re: Front light positition

Postby Oldjohnw » 26 Sep 2019, 7:05am

Debs wrote:Yonks ago i knew someone who's light-bracket on a folk leg came loose; the light and bracket swivelled around into spokes and jammed the wheel, he went over the handlebars face first into the road knocking out a few teeth.

Seems odd that bicycle design has not incorporated a 'universal' light attachment on the head-tube, seems like a good place to put a light.


In my childhood bikes were fitted with just such a bracket and the lamp had a slot which fitted into this.
John

tatanab
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Re: Front light positition

Postby tatanab » 26 Sep 2019, 7:27am

Debs wrote:Yonks ago i knew someone who's light-bracket on a folk leg came loose; the light and bracket swivelled around into spokes and jammed the wheel, he went over the handlebars face first into the road knocking out a few teeth.
I can see how that might happen with a clamp on bracket, but not the more usual (except on utility bikes like 3 speed hub roadsters) brazed on fitting.

Seems odd that bicycle design has not incorporated a 'universal' light attachment on the head-tube, seems like a good place to put a light.
The headtube is not a good idea because in generations past riders routinely used capes in the rain, some still do, and in other countries it is common amongst utility riders. it would also preclude the use of bar bags or wicker baskets for example. Perhaps this is why it used to be common on continental European to have a dynamo light fitted near the tip of the front mudguard. Having tried that I can say that it is not a good location because it gets covered in all sorts of dirt from the front wheel. Ergo, there is no universal solution.

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Sweep
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Re: Front light positition

Postby Sweep » 26 Sep 2019, 7:28am

francovendee wrote:I use a lot of tracks so does a fork mounted light show up the potholes more clearly? I have cycled in the dark without lights for about a mile along a farm track and not seeing the holes was quite dangerous. :oops:

Am always worried by Having anything that might end up in the wheels.
Can someone recommend a good battery light and mount for achieving this, particularly cat eye?
Have been doing some middle of the night descents on country lanes recently and more light might be handy.
Sweep

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mjr
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Re: Front light positition

Postby mjr » 26 Sep 2019, 11:29am

I'm with Mick F. I also used to commute with an old halogen plastic "miner's lamp" on the front fork. There were many bad things about those lights compared to modern LED dynamo ones, such as difficulty of keeping them watertight and keeping the batteries in place as I skittered along country lanes, but shadows thrown by the wheel was never one. I'm unsure what Brucey's lamp, fork and/or wheel did to cause that, but don't let one bad implementation set you against the concept - even if I prefer the crown (protected by a mudguard), the leg is still far better than a light mounted too high, not straight and not level on a crowded handlebar. Handlebars are for hands.

Brucey wrote:
mjr wrote:
Brucey wrote:FWIW most motorcyclists live in fear of being SMIDSY'd and they are lit up like a christmas tree.

And being lit up like a tree doesn't seem to be working for them, so I'm not sure that's a great argument!


my point is that most motorists are looking out for cars not two wheelers of any kind, and making yourself less visible by having a lamp that can be obscured from some angles isn't going to help matters one bit.

And my rebuttal is that few lamps are as easily obscured as you are suggesting.

Brucey wrote: Riding around with only a fork-mounted lamp that is definitely obscured from certain angles is not going to improve your life expectancy.

It'll certainly improve it more than riding around without any lights! Of course, don't mount it high enough that the top of the rim will block the lamp over a wide area of other road user head heights, but the obscuring of a lamp mounted low on the fork will be minimal and fairly far ahead of the bike. Oh and I just remembered: for the above to apply, it's important that the illuminated surface area (lens or reflector, depending on design) is wider than the tyre!


not quite as simple as that; the reflector/lens is usually designed to throw a beam of some kind and there is no guarantee that light thrown from the periphery of the lens/reflector is going to be thrown anywhere other than forwards. In many cases the light that emerges at an angle to the main beam (and renders you visible at an angle from side turnings) only comes from a small proportion of the light. You can gauge if this is the case by looking at the shadow that is cast by the front wheel; a well defined shadow essentially means a small effective emitter. Anyone within the shadow area won't be able to see the light. If the light emits strongly at an angle over the full diameter of a large lens then there would be no real shadow. IME this never happens, and worse yet deep aero section rims and fatter tyres mean the rim/tyre is more than ever capable of obscuring a fork mounted light.

The light reaching motorists' eyes should never be from the main beam on a standard light... well, not unless the motorist is in a very low sports car with their eyes below the cutoff height. The light they see is always from the so-called spill (that which illuminates reflective road signs) that basically appears as the glowing lens/reflector face, which is why I say it's important for that face to be wider than the tyre. That width is essentially why the front wheel throws no full shadow, only penumbra.

If you use a fork boss for a lamp there is usually a shadow cast at an angle of twenty or thirty degrees to one side.

Thirty degrees? That seems to mean that your fork lamp boss is wide or high or projects a long way forwards:

Distance of 622mm tyre bead in front of a low lamp mounting point on a typically-raked fork = 300mm

Width of front hub between dropouts = 100mm
Width of example front tyre = 32mm
So the left edge of the light is (100+32)/2 mm = 66mm to the right of a plane touching the left edge of the tyre.

Projecting a line back thirty degrees from there until it is 300mm back puts it (300 / √3)mm = 173mm right of that plane = 107mm right of the dropout.

I don't remember seeing many fork mounts that put the left edge of the lamp that far out - most are pretty close to the leg.

Of course, if you put the light higher up or used deeper rims, it wouldn't need to be mounted so far out before the wider sloped section of the tyre/wheel could block a wider lamp face, which is why I say mounting low (the centre third of the wheel height, say) is important.

My suggestion is that if you use a lamp like this, add a flashing LED or something higher up, that can be seen; it might save your life. If you use a fork mounted lamp only, from choice, then IMHO you are taking a pointless risk.

"it might save your life"? I've been a big fan of some of Brucey's technical posts, but I am really disappointed to read such scaremongering being used to try to support geometry that just doesn't stack up.

My suggestion is to prefer a fork crown mount, but if you need to use a traditional leg mount for some reason, then prefer a wide-faced lamp mounted low. Don't bother with pointless blinkies - they're just another light to look after for little benefit because anyone who doesn't see a lamp you can see with probably isn't looking anyway, so won't see a handlebar blinky either. Spend the time and money addressing real risks instead.
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
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pwa
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Re: Front light positition

Postby pwa » 26 Sep 2019, 11:36am

The height difference between a fork mounted light and one on the bars is not always very much. With the bracket I use in front of the stem clamp I can have the actual lamp top level with the underside of the bars. That leaves it not a lot higher than a fork mounted lamp on a riser bracket. The choice between the two, for me, was partly dictated by which would give the clearest beam avoiding my bar end gear lever cables, which are quite low.

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Re: Front light positition

Postby mjr » 26 Sep 2019, 11:40am

pwa wrote:The height difference between a fork mounted light and one on the bars is not always very much. With the bracket I use in front of the stem clamp I can have the actual lamp top level with the underside of the bars.

Yes, you could add brackets like that. I don't think that's really mounted "on the bars" any longer then. Personally, I think most such brackets I've seen look very ugly, but each to their own!
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
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pwa
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Re: Front light positition

Postby pwa » 26 Sep 2019, 11:47am

mjr wrote:
pwa wrote:The height difference between a fork mounted light and one on the bars is not always very much. With the bracket I use in front of the stem clamp I can have the actual lamp top level with the underside of the bars.

Yes, you could add brackets like that. I don't think that's really mounted "on the bars" any longer then. Personally, I think most such brackets I've seen look very ugly, but each to their own!

It is this one. Same lamp too.

https://www.sjscycles.co.uk/lighting-sp ... g-bracket/

Actually the top of the lamp is about level with the centre of the bars, as I have it with the bracket pointed more down and the lamp tilted back to the max.

I looked at the bike from the front before buying the bracket and it seemed to me that a fork mounted lamp would not be a lot lower but would cast more wheel shadow. And crucially, my cables would be in the way of the beam. That will vary from bike to bike. On some bikes the fork crown mounting position might have less cable in the way of the beam.

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Re: Front light positition

Postby Brucey » 26 Sep 2019, 11:58am

mjr wrote: ,,,,,


goodness me that is a lot of talk;

a) most lamps cast shadows as I have described
b) just look at them!
c) just look at where lamps end up on (or near) these brackets; 'centre third'...? They'd be no good for the reasons I have described if they did end up in the centre third, but they hardly ever end up there anyway.

some examples;

Image

Image

If you were to advocate dangling a large curved thing in front and slightly to one side of every front light, regardless of its position, you would soon be dismissed as a nut-job. Just because it was once considered acceptable to mount (glow-worm) lights on fork blade brackets doesn't mean it is a good idea.

You will note that I added a caveat to my comments; 'if you want to be seen'. Maybe you don't?

cheers
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mjr
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Re: Front light positition

Postby mjr » 26 Sep 2019, 12:51pm

Brucey wrote:
mjr wrote: ,,,,,


goodness me that is a lot of talk;

a) most lamps cast shadows as I have described
b) just look at them!
c) just look at where lamps end up on (or near) these brackets; 'centre third'...? They'd be no good for the reasons I have described if they did end up in the centre third, but they hardly ever end up there anyway.

It's geometry and maths, not talk. I have looked at them. I have used them. They do not necessarily throw shadows of the type you describe and if they did, it would almost never be at 30°.

Congratulations on finding some pictures of badly-mounted lights! Both those lights seem to be designed for mounting on fork crowns. The bullet light seems to be sitting above a bracket designed for hanging an old "miner's lamp" style light from (so ends up far too high, with the top of the wheel in the way), while the modern one looks to be on some sort of high pannier boss (so also ends up far too high).

The claim of a shadow at 30° was nonsense and those lamp/mount combinations are also silly. You can mount almost any lamp badly if you try hard enough. That doesn't make lamp or mount necessarily bad.
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
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Brucey
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Re: Front light positition

Postby Brucey » 26 Sep 2019, 1:27pm

mjr wrote:
Congratulations on finding some pictures of badly-mounted lights! Both those lights seem to be designed for mounting on fork crowns...


they were literally the first images of such lamps I found. The first one is very typical of such installations at one time. The second one has been mounted with an attempt to lower it; the boss hasn't even been used. It is still crap.

The claim of a shadow at 30° was nonsense and those lamp/mount combinations are also silly. You can mount almost any lamp badly if you try hard enough. That doesn't make lamp or mount necessarily bad.


I've seen and used many such arrangements on a fork boss and they all cast shadows, every single one of 'em. Obviously every single one allows the light to be almost wholly obscured, too. The exact angle of the shadow doesn't really matter; it just alters the speed of the other road user that won't see you. In a nutshell it is basically a daft idea to mount a light on a fork boss when there are alternatives.

If anyone is reading this and wondering if a light will or won't cast a shadow, just cut out a piece of cardboard that is rim/tyre shaped and dangle it in the relevant place. If you want to simulate the whole fork boss lamp experience, mount the cardboard permanently.... :roll:

cheers
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scottg
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Re: Front light positition

Postby scottg » 26 Sep 2019, 3:07pm

Mick F wrote:I don't remember shadow issues at all.
Many thousands of miles commuting in the dark.

No doubt there was a shadow, but it mattered not a jot.


I used B&M Cyo and Cyo Premiums with a fork boss, beam hits the
ground in front of the wheel, so little shadow. Also the the low shaped
beam was good a picking out pot holes and frost heaves.
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Mick F
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Re: Front light positition

Postby Mick F » 26 Sep 2019, 3:07pm

This is the only photograph I have of Mercian with lights fitted. Click a couple of times to zoom in.
Excellent Soubitez BB dynamo with a voltage regulator and a halogen front bulb.
If the front light is badly positioned, I'll eat my hat.

If the front light is badly positioned, what about the rear lamp? :lol: :lol:

Rowardennan.jpeg
Mick F. Cornwall

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mjr
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Re: Front light positition

Postby mjr » 26 Sep 2019, 3:09pm

The second lamp Brucey showed is very clearly on a high front pannier boss, unless I'm being shown a different photo.

Even simpler than dangling cardboard is to strap a suitable wide lamp by the low pannier mount on a fork leg. I did and took some measurements. A wide penumbra is cast, not full shadow, but if I cover part of the light, I can make it full shadow. That full shadow is at about 12° off straight, which I think make the 'constant bearing' calculations marginal. I think if you're doing 16mph, a motorist approaching a junction would have to be doing about 4mph for the light to be in that shadow the whole way. Almost no motorists are driving around at 4mph! This is not a reasonable risk to worry about and can be avoided in any case by not covering part of the lamp!

Car cabin pillars are a much bigger hazard.
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
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Brucey
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Re: Front light positition

Postby Brucey » 26 Sep 2019, 3:18pm

Mick, the rear light being obscured in a similar way on your bike is less of a worry; from any reasonable distance the various reflectors will show up far more clearly (to the driver of another vehicle with headlights) anyway. IME the triangular reflector on the saddlebag usually shows up most clearly, of the parts on your bike.

Its not clear in the picture but your front light might be high enough to be seen OK from side turnings. Even if low down and to one side, any shadow cast by the wheel would still irritate me though, not least because it could be easily avoided using a different mounting.

MJR, a shadow cast at 12 degrees is just annoying; so is the flickering from the shadows of the spokes. If you ride a couple of hours at night it just makes your eyes more tired than they need be if the illumination isn't fairly even. FWIW cars pull up to and through junctions at ~4mph often; as I said before the exact angle just changes the way in which you are less likely to be seen.

cheers
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Brucey
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Re: Front light positition

Postby Brucey » 26 Sep 2019, 3:30pm

mjr wrote:The second lamp Brucey showed is very clearly on a high front pannier boss, unless I'm being shown a different photo.


yes as I mentioned there is a fork boss, and had they used it, the lamp would be even higher up, but still not so high that it would be seen over the top of the tyre, I think.

BTW another significant irritation with the boss-mounted lamp position is that the side of the tyre (and the spokes) are comparatively well illuminated, and since these can be seen when riding it is another distraction, much like having cables in the way of the lamp can be.

cheers
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